Synthetic fibers having improved antistatic properties

ABSTRACT

Shaped objects including synthetic polymeric fibers with improved antistatic properties are prepared by incorporation therein about 1 to about 15% of a polyester antistatic agent prepared by reacting an N,N-bis(hydroxyalkyl) taurine salt with an organic polycarboxylic acid. Incorporation of the polyester into a synthetic polymer is accomplished by the process of preparing a melt or solution of the synthetic polymer and the polyester and extruding from the melt or casting from the solution to provide films, fibers and other molded objects exhibiting antistatic properties. A process for the preparation of the polyester antistatic agents of the invention, and for the preparation of the N,N -bis(hydroxyalkyl) taurine salts is also disclosed.

This is a division of application Ser. No. 859,359, filed Dec. 12, 1977,now abandoned; which is a divisional application of Ser. No. 739,497,filed Nov. 8, 1976, now U.S. Pat. No. 4,080,315 issued Mar. 21, 1978.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to man-made fibers and other molded objectsprepared from synthetic polymers having durable antistatic properties.

2. Description of the Prior Art

Generally, antistatic synthetic fibers, in the form of continuousfilament or spun yarns are obtained by first melt-spinning a linearfiber-forming synthetic polymer in combination with an antistatic agent.It has often been suggested that antistatic polymer fibers, such aspolyamide fibers, can be produced by melt-spinning a mixture of thefiber-forming polymer with such antistatic agents as polyalkylene oxidesor their reaction products. For instance, suitable tetrol compounds canbe chain extended for use as antistatic additives as described in U.S.Pat. No. 2,979,528.

It is known from the teachings of U.S. Pat. No. 3,147,301 that organicpolymers can be modified to impart a slightly ionic or hydrophiliccharacter thereto and to improve the dyeability and antistaticproperties of the polymer by the use of sulfo-organic esters of fumaricand maleic acids. Such esters contain the salt of a sulfonic acid. InU.S. Pat. No. 3,894,077 there is disclosed a nitrogen containingantistatic agent for a plastic comprising a compound of the formula##STR1## wherein R₁ is a hydroxyalkyl group of the formula ##STR2## inwhich R₄ is an alkyl group having 6 to 16 carbon atoms, R₂ is a loweralkyl group having 1 to 4 carbon atoms or hydroxyalkyl group of the samekind as R₁, R₃ is a lower alkyl group having 1 to 4 carbon atoms and mis an integer of 1 to 4. Partly because such antistatic agents forplastics are not polymeric, these compounds are not permanent and tendto be removed by exposure to washing or drycleaning solvents.

The antistatic agent compounds utilized as reactants herein aredisclosed in U.S. Pat. No. 2,830,082. These compounds areN-(hydroxyalkyl) taurine compounds having the following structure:##STR3## wherein R is a member of the group consisting of hydrogen andalkali metals, R' is a member of the group consisting of hydrogen, themethyl radical and hydroxyalkyl radicals containing from 2 to 4 carbonatoms. These compounds also lack permanence to washing and drycleaningof the antistatic effect when they are incorporated in a textile fabric.Because they are derived from taurines these compounds are moreexpensive to prepare than many other antistatic agents presentlyexisting in the prior art.

In German Pat. No. 2,318,308 there is disclosed an antistatic agent forpolyamide fibers which is a polyoxyalkylated amino acid. Thesecompositions can contain monovalent groups of the formula: ##STR4## inwhich X and Y are oxyalkylene units, R is an aliphatic, aromatic orcycloaliphatic group, Z is --COO-- residue, --SO₂ O-- residue or a metalsalt, x is 1 to 1,500 and y is 0 to 1,500. These materials attempt tocombine the increased conductivity of polyoxyalkylated compounds withthe polarizing effects of amine, carboxylate, sulfonate or other saltgroups. While these materials can be of high molecular weight, suchmaterials differ from the antistatic agent polyester compositions of theinvention which contain repeating amino and sulfonate salt groupingsalong the polymer chain, thus making it possible to incorporate agreater proportion of amino and sulfonate groups in the molecularstructure and obtain the advantages attendant thereon.

Generally, antistatic agents are incorporated in plastic materials,especially fibers, by processes which either involve impregnating thesynthetic polymer fiber, for instance, a polyamide fiber subsequent toits being woven into a fabric or alternately by incorporating theantistatic agent into the polymer melt prior to spinning into filaments.Fibers extruded from such a melt are believed to contain the additive asan insoluble phase in the form of fine fibrils aligned with anddispersed throughout the fiber. Desirable fiber properties are generallynot altered by the use of minor amounts of such additives, however, asubstantial reduction in their tendency to acquire a static charge canresult by the incorporation of an antistatic agent therein.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide (1) novel polyesterantistatic agents for polymeric shaped objects especially textilefibers, (2) novel polyesters having improved antistatic properties, (3)a process for the production of said agents, (4) a process for theproduction of antistatic shaped objects such as synthetic fibers, and(5) a process for the production of N,N-bis(hydroxyalkyl) taurine salts.The polyester antistatic agents can be incorporated into, for instance,a polypropylene fiber prior to melt-spinning into fibers. It has beenfound that the incorporation of both amino and sulfonate groups alongthe backbone of an oligomeric polyester antistatic agent provides adesirable balance of properties such that satisfactory antistaticproperties are obtained upon incorporation of said agent in a polymericshaped object.

DETAILED DESCRIPTION OF THE INVENTION

The amphoteric amino sulfonate salt reactants of the invention are knownfrom U.S. Pat. No. 2,830,082 as previously indicated. However, it hasnow been discovered that a more economical process for the preparationof such amphoteric amino sulfonate salts can be utilized to prepare suchcompounds rather than the prior art route of preparation from an alkalimetal salt of taurine or N-methyltaurine with a 1,2- or 2-3-alkyleneoxide having 2 to 4 carbon atoms.

The novel process of the invention for the preparation of amphotericamino sulfonate salts (N,N-bis(hydroxyalkyl) taurine salts) comprisesthe reaction of excess dialkanolamine with an alkali metal or alkalineearth metal salt of a hydroxyalkylsulfonic acid corresponding to thegeneral formula: ##STR5## wherein R₁, R₂, R₃, and R₄ can be the same ordifferent hydrocarbon radical selected from the group consisting ofaliphatic hydrocarbons having about 2 to about 12 carbon atoms and M isan alkali metal or an alkaline earth metal derived cation.Representative hydroxyalkylsulfonic acids from which these salts areprepared by known methods are as follows:

2-hydroxyethanesulfonic acid (isethionic acid),

2-hydroxy-1-propanesulfonic acid,

1-hydroxy-2-propanesulfonic acid,

2-hydroxy-1-butanesulfonic acid,

1-hydroxy-2-butanesulfonic acid,

3-hydroxy-2-butanesulfonic acid,

1-hydroxy-2-methyl-2-propanesulfonic acid,

2-hydroxy-2-methyl-1-propanesulfonic acid,

1-hydroxy-3-methoxy-2-propanesulfonic acid,

2-hydroxy-3-methoxy-1-propanesulfonic acid,

1-hydroxy-2-octanesulfonic acid,

1-hydroxy-2-dodecanesulfonic acid,

1-hydroxy-2-hexanedecanesulfonic acid,

2-hydroxycyclohexanesulfonic acid.

The hydroxyalkylsulfonic acids listed above are used in the form oftheir alkali metal or alkaline earth metal salts such as the sodium,potassium, calcium, magnesium, etc. These salts are readily prepared byneutralization of the hydroxysulfonic acid with an equivalent amount ofan alkali metal or alkaline earth metal hydroxide or carbonate.

The amphoteric amino sulfonate salt reactants are prepared by reactingat least 1 mole of a hydroxyalkylsulfonic acid metal salt with 2 or moremoles of a dialkanolamine in the presence of a catalytic amount of astrong base at a temperature of about 180° C. to about 200° C. The waterof condensation is removed during the process so that there is obtainedupon completion of the reaction the desired amphoteric amino sulfonatesalt. This is further reacted with an organic polycarboxylic acid toproduce the polyester antistatic agents of the invention. Suitablestrong base catalysts are the alkali metal hydroxides and carbonatesillustrated by sodium hydroxide, potassium hydroxide, lithium hydroxide,sodium carbonate, and potassium carbonate. The alkaline earth metalhydroxides and carbonates and the alkali metal alkoxides having 1 toabout 4 carbon atoms are also useful. Representative examples are sodiummethoxide, potassium methoxide and magnesium and calcium hydroxides,magnesium and calcium carbonates.

The dialkanolamines have the structural formula:

    HN(CH.sub.2 CHROH).sub.2

wherein R is a hydrogen atom or an alkyl radical having 0 to 21 carbonatoms. Non-limiting examples of the dialkanolamines are:

diethanolamine, dipropanolamine, diisopropanolamine,

2,2'-iminodibutanol-1, 3,3'-iminodibutanol-1,

4,4'-iminodibutanol-1, di-tertiary-butanolamine, and

3,3'-iminodipentanol-1, 6,6'-iminodihexanol-1.

Such dialkanolamines can be prepared by several methods well known tothose skilled in the art. One method is by the direct addition reactionbetween ammonia and an epoxy compound such as ethylene oxide orpropylene oxide. Another less direct process involves the reactionbetween ammonia and a halogenated alcohol such as 2-chlorobutanol-1.

The polyester of the invention comprises the reaction product of asubstantially equivalent amount of a polycarboxylic acid or mixturesthereof with an amino amphoteric sulfonate salt (N,N-bis(hydroxyalkyl)taurine salt) having the generalized formula: ##STR6## wherein R and R₁are alkyl and individually selected from alkyl groups having about 2 toabout 8 carbon atoms, and M is a metal selected from the groupconsisting of an alkali metal, an alkaline earth metal and mixturesthereof.

In the preparation of the polyester antistatic agent of the invention,the amphoteric amino sulfonate salt reactant prepared is further reactedwith an organic polycarboxylic acid reactant. Said reactant is definedas any aliphatic, cycloaliphatic or aromatic polycarboxylic acidanhydride, ester and acid halide or mixtures thereof. Examples of suchacids are phthalic, terephthalic, isophthalic, trimellitic,pyromellitic, oxalic, malonic, succinic, glutaric, adipic, pimelic,suberic, azelaic, sebacic, maleic, and fumaric acids. Also useful are1,3-cyclopentane dicarboxylic, 1,2-cyclohexane dicarboxylic,1,3-cyclohexane dicarboxylic, 1,4-cyclohexane dicarboxylic,2,5-norbornane dicarboxylic, 1,4-naphthalic, diglycolic,thiodipropionic, and 2,5-naphthalene dicarboxylic acids. Suitablemixtures of these polycarboxylic acids can be utilized to obtain optimalphysical properties in the polyester composition of the invention as iswell known by those skilled in the art. The corresponding acidanhydrides, esters and acid halides, i.e., acid chlorides of the aboveenumerated polycarboxylic acids can also be used.

The novel polyester of the invention is uniformly dispersed into shapedpolymer such as a fiber-forming polymer and spun into fiber by methodswell known in the art to produce an antistatic fiber. Generally, thenovel polyester is incorporated into a shaped polymer fiber in theproportions of from about 1 to about 15%, preferably about 3 to about10% by weight.

Generally, the polyester antistatic agent is added to the polymerizationreactor at elevated temperature under an inert atmosphere during thelast 30 minutes of the polymerization of the polyamide or other polymerwhich is desired to be rendered antistatic. The agent is thoroughlymixed into the polymer with stirring. The mixture is then extruded inthe desired form, cooled, washed and dried.

The following examples will further illustrate the nature and method forpreparing the polyester antistatic agents of the invention and fortreating synthetic fiber-forming polymeric materials therewith. Theseexamples, however, are not to be considered as limiting the invention.In the specification, claims and the examples which follow allproportions are by weight and all temperatures are in degrees centigradeunless otherwise noted.

EXAMPLE 1

An amphoteric amino sulfonate salt was prepared as follows:

Into a two-liter, three-necked flask equipped with a mechanical stirrer,thermometer, thermometer well and a vacuum distillation take-off therewas charged 470 grams of 97% ethanolamine, 331 grams of isethionic acid,sodium salt (2-hydroxyethanesulfonic acid sodium salt) and 1.5 grams ofsodium hydroxide. The resulting slurry was warmed to 60° C. and brieflyplaced under a pressure less than or equal to 5 millimeters of mercury.The vacuum was relieved with nitrogen in order to deoxygenate themixture and the entire reaction was conducted under a nitrogen blanket.The flask was heated so as to evolve water, the evolution of waterbeginning at 180° C. The temperature was slowly increased over a periodof 8 hours to a temperature of 195° C. to facilitate removal of water.The theoretical amount of water of condensation (36 grams) had beencollected after a period of 8 hours. The mixture was then cooled to 165°C. and the above vacuum established. Rapid removal of diethanolamineoccurred at a temperature of 139° C. and at a pressure of 0.1 millimeterof mercury. At a pot temperature of 165° C., a total of 236 grams ofdiethanolamine was removed. In order to distill out the remainder of thediethanolamine, the pot temperature was increased to 180° C. Another 47grams of distillate was obtained bringing the total of unreacteddiethanolamine to 258 grams. The product had a hydroxyl number of 469and 6.3% nitrogen. This compares with a calculated theoretical value of479 for hydroxyl number and 5.8 for percent nitrogen.

EXAMPLE 2

The antistatic agent polyester of the invention was prepared using theamphoteric amino sulfonate salt prepared in Example 1 by the followingprocedure:

A 500-milliliter, three-necked flask equipped with a mechanical stirrer,thermometer and complete with a vacuum distillation take-off consistingof a Claisen head with thermometer, condenser, vacuum adaptor andreceiving flask was charged with 334 grams of a 66% aqueous solution ofthe amphoteric amino sulfonic salt prepared in Example 1. To this flaskthere was then added 143 grams of azelaic acid. The mixture wasdistilled under reduced pressure to remove water. After one hour all thewater had been removed and the temperature was increased until water ofcondensation appeared. At a temperature of 140° C. to 160° C. and apressure of 0.5 millimeter of mercury, rapid evolution of water ofcondensation was noted by vigorous bubbling and condensation of water inthe condenser and receiving flask. After a reaction time of 3 hours, thehomogeneous, viscous and transparent reaction product was dischargedfrom the flask, and on cooling solidified into a hard and brittle resin.The product had an OH number of 44 and an acid number of 57.

EXAMPLE 3

The procedure of Example 2 was repeated except that sebacic acid insteadof azelaic acid was utilized to produce an antistatic agent polyesterhaving an OH number of 6.4 and an acid number of 79.

EXAMPLE 4

The reaction procedure of Example 2 was repeated using adipic acidinstead of the azelaic acid used in Example 2 to produce a polyesterhaving a hydroxyl number of 22 and a acid number of 70.

EXAMPLES 7 and 8

Resistivity determinations in accordance with ASTM D-257 test methodwere made using a Keithly electrometer and static detector. Polyamidefilms containing the polyester antistatic agent of the invention wereprepared by dissolving the polyamide (sold under the trademark "Nylon6") and the polyester in trifluoroethanol and casting film samplestherefrom containing five percent and ten percent of the polyesterantistatic agent of the invention. Resistivity determinations were madeunder controlled temperature and humidity and results obtained at 25° C.at ten, twenty and thirty percent relative humidity. Results are shownin Table I.

                  TABLE I                                                         ______________________________________                                        RESISTIVITY OF POLYAMIDE FILM                                                 CONTAINING THE                                                                ANTISTATIC AGENT OF THE INVENTION                                                     %        Resistivity, Log.sub.10                                              Antistatic                                                                             Relative Humidity (%)                                        Example   Agent      10       20     30                                       ______________________________________                                        7         5          14.8     14.0   12.9                                     8         10         13.9     13.0   12.2                                     Control   0          14.3     13.7   13.2                                     ______________________________________                                    

EXAMPLE 9

The polyester antistatic agent of the invention prepared in Example 2was used to prepare an antistatic polypropylene fiber by incorporationof about one percent by weight thereof in a polypropylene polymer priorto extrusion into filaments. Samples of polypropylene were extruded bothwith and without the polyester prepared in Example 2 using a CSIMax-Mixing Extruder. Samples of fiber obtained were conditioned at 10,20 and 30 percent relative humidity at 25° C. and then surfaceresistivity was measured as described in Examples 7 and 8. All sampleswere conditioned for 72 hours at 10 percent relative humidity at 25° C.Those to be tested at this condition are evaluated and the remainder ofthe samples are further conditioned at 20 percent relative humidity for24 hours. Samples to be evaluated at 30 percent relative humidity arefurther conditioned at this condition for 24 hours prior to testing.Results are shown in Table II.

                  TABLE II                                                        ______________________________________                                        RESISTIVITY OF POLYPROPYLENE FIBER                                            CONTAINING THE                                                                ANTISTATIC AGENT OF THE INVENTION                                                     %        Resistivity, Log.sub.10                                              Antistatic                                                                             Relative Humidity (%)                                        Example   Agent      10       20     30                                       ______________________________________                                        9         1          13.7     13.6   12.2                                     Control   0          14.4     14.6   14.6                                     ______________________________________                                    

While this invention has been described with reference to certainspecific embodiments, it will be recognized by those skilled in the artthat many variations are possible without departing from the scope andspirit of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A synthetic polymericfiber having incorporated therein about 1 to about 15 percent by weightof a polyester antistatic agent prepared by reacting anN,N-bis(hydroxyalkyl) taurine metal salt with an organic polycarboxylicacid reactant.
 2. The fiber of claim 1 wherein said organicpolycarboxylic acid reactant is selected from the group consisting ofaliphatic, aromatic, cycloaliphatic polycarboxylic acids and anhydridesand mixtures thereof and said polymeric fiber is a polyamide or apolypropylene fiber.
 3. The fiber of claim 1 wherein saidN,N-bis(hydroxyalkyl) taurine metal salt has the formula: ##STR7##wherein R and R₁ are alkyl and individually selected from alkyl groupshaving about 2 to about 8 carbon atoms and M is a metal selected fromthe group consisting of the alkali metals, alkaline earth metals, andmixtures thereof.
 4. The fiber of claim 2 wherein R₁ is ethyl and M isan alkali metal.
 5. The fiber of claim 4 wherein said polycarboxylicacid is selected from the group consisting of azelaic acid, sebacicacid, adipic acid and mixtures thereof.
 6. The fiber of claim 5 whereinsaid polycarboxylic acid is azelaic acid.